Telecommunication circuit networks essentially consist of electronic devices arranged in a system. This system provides for a front panel consisting of a face plate, printed circuit board (PCB), a latch mechanism on either side of the face plate to fasten the front panel with the chassis. The face plate area through the openings is the access point to the services offered by the PCB. At times the front panel comprising of PCB, a latch mechanism on either side, is often referred to as the field replacement unit (FRU) or card. An FRU/card performs certain specific functions which includes providing support to the entire telecommunication network system. Hence a telecommunication network system may require a number of such cards arranged in a particular sequence enabling to co-ordinate the specific functions of each card so as to support the telecommunication network system. The above FRU/card is often needed to be removed and fixed for up-gradation of services offered by the FRU, a routine check or for servicing the FRU. The FRU is fastened to the chassis or enclosure through the card cage by a fastening mechanism comprising of a floating captive screw on the sides of the face plate.
Floating captive screws are commonly used to fasten removable covers or enclosures when it is desired to keep the screw in position without losing it. A captive screw generally is fitted in housing, for example, a panel. A screw is inserted through the housing and retained therein such that the housing retains the screw even when the screw is not engaged in a threaded bore or receiving nut. These screws owing to its floating nature couple with the floating nuts provided on the card cage with a given allowable offset range. At times it so happens that, the floating captive screw because of its floating nature is inclined or oriented to an extent where it misaligns with the receiving nut provided on the card cage and at times there is complete mismatch of alignment between the screw axis and the receiving floating nut. Further the threaded portion of the captive screw is always projected towards the card cage within the chassis and so the projection of the threaded portion between the face plate and the card cage causes the FRU to misalign or incomplete insertion or jack-in thereby giving rise to improper attachment of PCB with the backplane of the system. Therefore one has to check the jack in every time an FRU is removed (or jacked-out) and replaced. Further there are chances that this captive screw may get stuck in its inclined position leaving a substantial threaded portion in-between the face plate and the card cage thus damaging the captive screw or face plate of FRU.
Once the captive screw gets damaged, the entire unit comprising of captive screw with the face plate has to be replaced which involves additional cost. Repeated jacking in and trying to couple the screw with the nut, in case of misalignment of captive screw with the floating receiving nut in the card guide may damage the chassis also. If the screw head is damaged due to repeated screwing and unscrewing, one has to replace the entire face plate assembly of FRU. Therefore a fastening mechanism providing for a detachable captive floating screw for effective fastening of two parts by aligning the captive screw with the receiving nut on the card guide is required.